Power supply system for a telecommunication system

ABSTRACT

An auxiliary power supply system includes an internal combustion engine driving an alternator the output of which is rectified and supplied to DC bus lines across which a storage battery is connected. The DC bus lines may supply a consuming device such as an uninterruptible power supply or telecommunications system. The voltage across the bus lines is sensed and when the voltage drops below a selected value, indicating that the consuming devices is drawing power from the battery beyond a desired limit, the engine is turned on for a period of time to warm it up, during which the power from the generator is not supplied to the DC bus lines. Thereafter, the generator supplies power to the DC bus lines to supply the consuming device and partially recharge the battery until the consuming device is no longer drawing power, after which the engine is shut off. The power supply system includes a controller which monitors the intervals of time between turn-ons of the engine and if a selected period of time is exceeded, the engine is started without supplying power from the generator to the DC bus lines to allow the engine and generator to warm-up, enhancing maintenance of the system. The operating characteristics of the engine and generator are sensed and stored for access by an operator and warnings are provided if these conditions exceed acceptable limits.

This is a continuation of Ser. No. 07/653,793 filed Feb. 11, 1991,entitled Auxiliary Power Supply System for Providing DC Power onCommand, now U.S. Pat. No. 5,198,698.

FIELD OF THE INVENTION

This invention pertains to power supply units suited to provide backupelectrical power in the case of failure of the primary power from asource such as the commercial power grid.

BACKGROUND OF THE INVENTION

Uninterruptible power supplies or systems (UPS) are coming into commonuse to backup the power supplied from the commercial power system tocritical loads such as computers, telephone systems or medicalequipment. In case of a black-out or disturbance on the commercial powersystem, the UPS takes over the supply of power to the critical loadduring the interruption. Although various designs are used for UPSsystems, they typically provide power during black-outs from a storagebattery through an inverter to the critical load during the time thatthe power system is down.

Because most UPS systems utilize a battery to provide the stored energyto power the critical load during black-outs, the run time for UPSoperation is limited by the storage capacity of the battery. Thus, themost straightforward present way of extending the UPS run time is simplyto use additional batteries. However, this approach has severaldifficulties. One is cost, since the number of batteries required isgenerally proportional to the desired run time. Moreover, increasing thenumber of batteries presents additional problems. Battery connectionsmust be kept tightened and free of corrosion, which increases themaintenance cost. To achieve optimum battery life, the batteries must bemaintained fully charged and at the proper temperature. Battery storagerooms often require special ventilation. Multiple strings of batteriesoften become unbalanced as they age. Large number of batteries alsooccupy valuable floor space and their weight may cause structuralloading problems. Furthermore, batteries commonly require replacement inthree to five years, which may be substantially less than the life timeof the UPS system as a whole, thus increasing the cost of the systemover its lifetime.

An alternative to the use of additional batteries to provide auxiliarypower to a critical load during long blackouts has been the use of agasoline fueled alternating current (AC) generator (alternator). ACgenerators have traditionally been used to provide backup power tocritical loads, including entire buildings, during long power outages inthe commercial power system. To avoid even a momentary interruption ofpower to critical loads, a UPS may be used to supply the critical loadsfor a short period of time, after which the gasoline engine of the ACgenerator is started, allowing the generator to take over the supply ofpower to the load. This may be accomplished by disconnecting the UPSfrom the load and directly connecting the AC generator to the loadduring prolonged power outages. In some UPS systems, the AC generator isswitched in to the input terminals of the UPS to substitute for thefailed line power during prolonged power outages. Such a connection ofthe AC generator is most typically utilized in double inverter UPSsystems in which the critical load is constantly supplied with powerfrom the UPS inverter even during normal operation.

The utilization of an auxiliary gasoline engine driven AC generator toprovide the backup supply power is useful but has certain disadvantages.Commonly, the gasoline engines which power the generator will not startwhen needed. The unreliability of the gasoline engine is particularly aproblem where the generator is at a remote location where frequentpreventive maintenance is not possible or convenient. Because suchstandby generators are only occasionally started to supply power to theload during power outages, the condition of both the engines andgenerators can deteriorate. For example, engines which run onlyinfrequently may be subject to corrosion problems caused bycondensation, lack of lubrication on bearing surfaces, and otherproblems associated with long term idleness.

If AC generators are utilized to provide power to a conventional doubleconversion UPS, the generators must typically be oversized by a factorof 2.5 to 3 times. Such oversizing is required because of the high crestfactor load created by the double conversion of the AC power to DC powerback to AC power. For example, a 10 kilowatt (KW) UPS generally willrequire a 25-30 KW AC generator. Additional costs are incurred for theinstallation and the cost of an automatic transfer switch.

If the critical loads are to be switched from the UPS to the ACgenerator, once it is up and running, the generator must be phase lockedand synchronized with the output of the UPS so as to maintain a smoothtransition. This transition is often difficult unless sophisticated andcostly electronics are utilized. Such electronics adds to the cost andcomplexity of the system, but a poor power transition can disrupt theflow of power to a particularly critical load, such as a computer, andcause it to malfunction.

A problem associated with the use of AC generators connected directly tothe load is that the AC generator output is often unstable, whichresults in additional system problems. To stabilize the frequency of theoutput, the engine/generator set is often oversized. Mechanical orelectronic speed governor systems are required, which add cost andcomplexity to the system and reduce reliability. If the load on the ACgenerator changes in magnitude or phase angle, the output waveform fromthe generator is often distorted. These distortions can affect theoperation of the more sophisticated UPS models, which examine sags intheir input waveform to anticipate outages and serious under-voltages.Such cyclic load-induced variations in generator waveforms can causesuch UPS systems to revert to battery operation frequently, even whenbattery power is not actually necessary to support the load. The resultis battery depletion and reduced backup capabilities.

AC engine/generator sets have also been utilized as auxiliary powersupplies for other applications where a UPS is not necessary, forexample, in telephone systems where the batteries which provide power tothe telephone networks are charged with rectified power from the ACpower lines. Auxiliary engine/generator sets may be utilized to providethe charging power to these batteries during power system failure.However, such engine/generator sets have been subject to the same typesof reliability and maintenance problems discussed above.

SUMMARY OF THE INVENTION

In accordance with the present invention, an auxiliary power supplysystem is provided which provides DC output power on demand to DC buslines such as those across which a battery is connected which supplypower to an uninterruptible power system, a telecommunication system, orother comparable DC load. The auxiliary power supply of the presentinvention includes an internal combustion engine connected to drive analternator which preferably provides polyphase output power to arectifier which converts the AC power to DC power. Filters arepreferably used to filter the rectified DC power to provide a low rippleoutput voltage to the DC bus lines.

The auxiliary power supply of the present invention is advantageouslyutilized with a UPS system which provides power to a critical loadduring momentary interruptions of power from the commercial powersystem. In such applications, the commercial power system wouldtypically provide AC power to the critical load during normal operationand would, either through a separate rectifier or though the UPS system,provide charging power to the storage battery to maintain the chargecondition of the battery. During such normal operation, the auxiliarypower system is not operating. Upon a power outage, the UPS systemoperates in the usual manner to supply continuous AC power to the loadwithout interruption. The controller of the auxiliary power system ofthe present invention monitors the operation of the UPS and the DCvoltage at the UPS battery and determines whether a long-term poweroutage has occurred and whether the battery supplying the UPS hassufficient reserve energy to supply power to the load. Upondetermination that auxiliary power will be needed to augment the batterypower supplied to the UPS, the engine of the auxiliary power system isstarted. For an initial warm-up interval, no power is supplied from theAC generator to the load. Upon adequate warm-up of the engine, therectified output of the alternator is connected to the DC bus lines bothto provide power to the UPS which is transferred to the critical loadand to recharge at least partially the storage battery. Because theauxiliary power generator provides its output power to the DC bus linesto which the storage battery is connected, there is no change in theoutput provided from the UPS during the switching-in of power from theauxiliary power system, and thus no disruption or disturbance in the ACpower supplied to the critical load.

It is a particular objective of the present invention to provide anauxiliary power system having a high reliability engine/generator set byappropriate exercising of the auxiliary power system and by monitoringof system conditions during the time that the system is being exercisedand during actual power supply operation. A computer controller withinthe auxiliary power system monitors the time elapsed since the lastturn-on of the system, which may have occurred during an exerciseoperation or during actual power supply operation. If the time elapsedexceeds a predetermined interval, the controller starts the engine torun the engine and generator set with power disconnected from the DC buslines. The engine is run for a time sufficient to properly exercise theengine and maintain adequate lubrication and condition of moving partsin both the engine and the generator. The length of time of running ofthe engine may be predetermined to achieve a desired system operatingcondition such as engine temperature. During the time that the engine isoperating, the controller preferably monitors several conditions of theengine and generator, including the date and time of the exercise cycle,the DC output voltage from the generator, the remaining fuel level inthe fuel tank of the engine, the battery voltage of the cranking batterythat provides the cranking power to turn on the engine, the engine blocktemperature, oil pressure, and the ambient temperature, and may alsomonitor conditions of the DC bus line, such as the voltage across the DCbus lines and thereby the condition of the main storage batterysupplying the UPS or the DC load. During exercise engine operation, thecontroller stores the values of the system conditions that weremonitored in non-volatile memory and makes such values available forread-out, either by an operator at the site of the auxiliary powersystem or through telemetry to a remote location. Moreover, thecontroller preferably compares the monitored system conditions withpredetermined set point conditions and provides an error or warningsignal if the sensed conditions are outside of the boundaries specifiedby the set points. This warning may be provided through an audible orvisual signal (or both) provided to the operator at the site or remotelyby telemetry. The sensing of system condition values which wouldindicate a serious malfunction of the system, such as over-temperatureof the engine, or very low fuel level, or deficient generator outputvoltage, will result in the controller shutting down the auxiliary powersystem and disconnecting it from the DC bus lines so that no damage isdone either to the auxiliary power system or to the components connectedto the DC bus lines. Such monitoring and control of the auxiliary powersystem operation is carried out both during the exercise cycling of theengine and during power supply operation where power is being providedto the DC bus lines.

The auxiliary power system of the invention preferably monitors thevoltage across the DC bus lines to determine if and when the engineshould be started to prepare to provide power to the bus lines. Duringnormal operation when the commercial power grid is supplying power tothe load and to the UPS to charge the battery, the voltage across the DCbus lines will be constant at a nominal value. Upon failure of linepower, the UPS automatically switches in to supply power from thebattery to the load. This results in a decline in the voltage across thebus lines as the battery is drained, generally in exponential decayingmanner. If the power outage is relatively short, the auxiliary powersystem need not be activated. When supply of power from the commercialpower system is resumed, the UPS will stop discharging the battery andpower can be provided from the commercial power system to the battery torecharge it. Relatively short power outages do not damage the batteryand allow it to be readily recharged to prepare for another powershortage. However, if the voltage across the DC bus lines drops below apredetermined value, indicating either that the power outage is of along duration or that the load on the battery through the UPS issufficiently great that the battery is being rapidly drained, the systemcontroller starts the engine of the auxiliary power system. However, therectified output voltage of the alternator is not immediately applied tothe DC bus lines. Rather, the engine is allowed to warm-up for a presetperiod of time so that when the output of the alternator is connected tothe DC bus lines the engine will be operating at normal conditions andthe alternator will be running at proper speeds so that the loading onthe engine as the alternator output is switched-in to the DC bus lineswill not adversely affect the operation of the engine or the alternator.When the output of the auxiliary power system is connected to the DC buslines, the voltage provided by the auxiliary power system is greaterthan the voltage level provided from the battery at that time, but notat the level of the fully charged battery voltage under normalconditions. At such output voltage levels from the auxiliary powersystem, the power through the UPS to the load will be provided entirelyfrom the auxiliary power system, and, in addition, the battery will bepartially recharged with power from the auxiliary system. The controllermonitors the output of the voltage across the DC bus lines and controlsthe output of the generator to maintain this voltage. Consequently, theauxiliary power supply cannot overcharge the storage batteries. Theauxiliary power system continues to provide power to the UPS (or otherDC load) for as long as necessary. When commercial line power returns,commercial power is provided to the critical load and the controllersenses the drop in the demand for load current on the DC bus lines andturns itself off. The battery charger within the UPS or an auxiliarybattery charger then provides DC power from the commercial power systemto the DC bus lines to bring the storage batteries back to full charge.Consequently, the auxiliary power system of the present invention servesto maintain the storage batteries at optimum charge withoutovercharging, and without the loss of water or electrolyte which wouldaccompany overcharging or excessive draining of the battery. The outputof the auxiliary power system is preferably voltage regulated andcurrent limited to protect the batteries and other equipment connectedto the DC bus lines. Output fuses prevent damage from accidentallyreversed connections to the external batteries.

The alternator utilized in the auxiliary power system is preferably ahigh frequency (greater than 60 HZ) polyphase brushless alternatorproviding its output to a rectifier and filter system to provideextremely smooth DC voltage to the DC bus lines. The smooth DC outputvoltage reduces the RMS magnitude of charging current to the batteries,and by precision voltage regulation across the DC bus lines, thebatteries are floated at the correct potential for optimum life of thebatteries.

Further objects, features and advantages of the invention will beapparent from the following detailed description when taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a block diagram showing a typical configuration in which ACgenerator sets have been used to provide auxiliary power to DC consumingequipment such as telecommunication systems.

FIG. 2 is a block diagram showing a typical configuration in which ACgenerator sets have been used to provide auxiliary power to DC consumingequipment such as telecommunication systems.

FIG. 3 is a block diagram showing a typical configuration in which ACgenerator sets have been used to provide auxiliary power to DC consumingequipment such as uninterruptible power supplies.

FIG. 4 is a block diagram showing a typical configuration in which ACgenerator sets have been used to provide auxiliary power to DC consumingequipment such as uninterruptible power supplies.

FIG. 5 is a block diagram showing a connection of the auxiliary powersystem of the present invention to an uninterruptible power supplysystem.

FIG. 6 is a block diagram illustrating the connection of the auxiliarypower system of the present invention to a telecommunications system.

FIG. 7 is a block diagram of the major components of the auxiliary powersystem of the present invention.

FIG. 8 is a graph showing the voltage across the DC bus lines to anuninterruptible power supply to which the auxiliary power system of thepresent invention is connected during a typical cycle of power outage.

FIG. 9 is a schematic circuit diagram of the alternator control systemand rectifier and filter in the auxiliary power supply of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

To best illustrate the utilization of the auxiliary power supply of thepresent invention, conventional connections of AC generators to DCconsuming loads are illustratively shown in block diagram form in FIGS.1-4. FIG. 1 shows a connection to a telecommunication system 15 whichreceives power from multiple batteries 16 connected between DC powerlines 18 and 19. The batteries 16 are charged normally from powerprovided from AC lines 21 through a transfer switch 22 to redundantchargers 23 the DC output of which is connected to the lines 18 and 19to charge the batteries 16. Upon failure of the power from the AC powerlines 21, the transfer switch 22 is switched to provide power from an ACengine/generator set 24 through AC power lines 25 and the switch 22 tothe chargers 23. The generator 24 is run as long as necessary tomaintain the charge on the batteries 16. A variation of this arrangementis shown in FIG. 2 in which the components are the same except that theoutput of the AC generator 24 is provided to a separate rectifier 26,the DC output of which is connected by lines 27 to the DC bus lines 18and 19. The AC generator can then supply power to the DC bus lines inparallel with the AC lines, although ordinarily the generator would notbe run as long as power is available from the AC power lines. Typical DCloads 15 are telecommunications systems, such as telephone systems,which use a relatively low DC voltage for operation.

Most power consuming devices are adapted to operate on alternatingcurrent such as that conventionally provided by commercial powersystems. To maintain continuity of power supplied to such loads,uninterruptible power systems have been developed which automaticallyprovide an AC output voltage to the critical load when power in thepower system fails, generally with a minimum disruption in the waveformof the voltage provided to the critical load. Typical prior arrangementsin which an AC engine/generator set are connected to an uninterruptiblepower system (UPS) are illustrated in FIGS. 3 and 4. As shown in FIG. 3,the UPS 30 which provides AC output on lines 31 receives AC input poweron a line 32 either from the AC power lines 33 or an AC generator 34,depending on the position of a transfer switch 35. Under normaloperation, the AC generator 34 is not operating and normal power isprovided from the line 33 through the switch 35. Upon power systemfailure, the UPS 30, which contains an internal storage battery (notshown), immediately provides AC output power which is supplied from theinternal battery. The AC generator 34 is then turned on and power issupplied from the generator through the transfer switch 35 to the ACinput lines 32 to the UPS. The UPS has an internal rectifier whichrectifies the AC voltage on lines 32 to a DC voltage which is invertedto the AC output, although some UPS systems have been built to operateso that the AC input power is directly connected to the AC output lines31. A common type of UPS system called a double conversion systemconverts the AC input power on lines 32 to a DC voltage which is appliedin parallel to the storage battery voltage, and the DC power is theninverted to an AC output power so that the output inverter operatescontinuously, even during normal power conditions on the AC output line.Other types of uninterruptible power supply systems do not have aconstantly running inverter to invert the DC input power to AC outputpower, but turn on the inverter only when power from the AC input linesfails.

A variation on the UPS architecture commonly used in the prior art isshown in FIG. 4. In this arrangement, the AC input lines 33 are directlyconnected to the normal AC input connection of the UPS where, forexample, in a double conversion system the internal rectifier of the UPSwould rectify this voltage to DC voltage which is applied across thebattery of the UPS. However, the output power on lines 36 provided bythe AC generator 34 is rectified by a rectifier 37 to a DC voltage whichis provided on DC output lines 38 to the UPS 30. This DC output voltagefrom the rectifier 37 would then be applied in parallel with the DCvoltage of the internal storage battery within the UPS 30.

In each of the foregoing systems, the AC engine/generator 24 or 34 is aconventional generator set which provides alternating current outputpower when needed but is not constantly running. Due to the long periodsof idleness between the times at which the generator is called upon tosupply power, deterioration of the generator sets can occur for thereasons described above, leading to reliability problems and the needfor excessive maintenance and monitoring of these systems. If thegenerators are intended to provide alternating current directly to theoutput lines, such generators must be designed (for typical operation inthe United States) to provide 60 HZ output power at desired outputvoltages (e.g., 120 V or 240 V), requiring provision for careful controlof output voltage, frequency and phase. Such requirements constrain notonly the generator but also the operation of the engine, and oftenrequire oversizing of the engine and generator to meet theserequirements.

In contrast, the auxiliary power system of the present invention isspecifically designed to provide DC output power at a controlled voltagelevel, utilizing rectification of the output of a generator, so that itis not necessary to control the output frequency or phase of thealternator but rather only the effective DC voltage level delivered fromthe rectified output of the alternator. Consequently, the control of thealternator is simplified and the size of the alternator and enginedriving it can be more appropriately sized to the maximum power outputrequired from the engine/generator set. The auxiliary power system ofthe present invention effectively acts as a regulated DC power sourceproviding a controllable DC output voltage under varying loadconditions.

Typical connections of the auxiliary power system of the presentinvention are shown in block diagram form in FIGS. 5 and 6. Withreference to FIG. 5, the auxiliary power system 40 of the inventionprovides output DC power, when activated, on DC output lines 41 and 42which are connected to DC bus lines 43 and 44. A battery or batteries 45are connected across the DC bus lines 43 and 44. The battery 45 may formthe internal battery of an uninterruptible power supply system 46 whichalso includes rectifier, inverter and control components representedcollectively by the block 47 in FIG. 5. These components receive ACinput power on lines 48 from the commercial AC power system and deliverAC output power on output lines 49 to the critical load. The UPS 46 maybe any type of UPS architecture, including a double conversion UPSsystem in which the AC input power 48 is rectified to a DC voltage levelapplied in parallel to the bus lines 43 and 44 and then constantlyinverted to an AC power on the lines 49, or a system in which in the ACpower on the lines 48 is transferred to the output lines 49 withoutbeing converted to DC power under normal conditions, for example, byusing a ferroresonant transformer between the input and output. The UPSsystem may also be of the type which directly connects the input poweron the lines 48 to the AC output lines 49 during normal operation, butprovides inverted power to the lines 49 from the DC bus lines 43 and 44during power outages on AC power lines 48. With each of these types ofsystems, the auxiliary power system 40 does not normally provide DCpower on the lines 41 and 42 as long as proper AC power is provided fromthe lines 48. When extended power outages occur on the lines 48, thesystem 40, as described further below, determines when an extended poweroutage has occurred or when the battery 45 cannot meet the demands ofthe load, and turns on to provide the DC power in the lines 41 and 42 totake over the supply of power to the UPS and thus supply power to theload.

The system of FIG. 6 utilizes the auxiliary power supply 40 with aconstant DC load, such as a telecommunication system 50, which normallyreceives power from the DC bus lines 43 and 44 across which the battery45 is connected. When AC power is available from an AC power system onpower lines 51, a charger 52 is operated to supply power on DC lines 53to the bus lines 43 and 44 to maintain a charge on the battery 45 andsupply power to the load 50. Upon failure of the AC power system, theauxiliary power system 40 is turned on to perform the duty of supplyingcharging power to the battery 45 and to the load 50.

A block diagram of the auxiliary power supply system 40 of the presentinvention shown illustratively connected to an uninterruptible powersystem (such as the UPS 46 of FIG. 5) is shown in FIG. 7. Power isprovided from an internal combustion engine 60 coupled by a shaft 61 toan alternator 62. The alternator 62 preferably provides polyphase (e.g.,three phase) output power on power lines 63 which are connected to abridge rectifier 64. A higher number of phases (e.g., 9 phase) may alsobe utilized, particularly where higher power output is required. Therectifier 64 rectifies the alternating current from the alternator andprovides DC output voltage on output lines 66 to a filter 67 whichfilters out the ripples in the rectified output voltage to provide arelatively constant output voltage on the output lines 41 and 42 whichare connected to the DC bus lines 43 and 44.

The monitoring and control of the auxiliary power supply is carried outby a microprocessor 70 with associated read only memory (PROM) 71 andrandom access memory (RAM) 72 under control of internal program in thePROM 71. The microprocessor receives operator input from an operatorcontrol panel 74, provides display of operating conditions and variousparameters on a visual display 75 which can be read by the operator, andcommunicates with remote devices 76 such as remote terminals connectedby a telephone line or other telecommunications connection.

The microprocessor 70 operating under the control of its internalprogram monitors the state and operating parameters of the system. Inparticular, the microprocessor monitors the voltage across the outputlines 41 and 42 and the DC bus lines 43 and 44 by lines 79 which areconnected to an analog-to-digital converter 80 which provides itsdigital output data indicative of the voltage across the DC bus to themicroprocessor 70. The microprocessor also receives readings on datalines 81 from engine status sensors 82, such as oil pressure and engineblock temperature sensors, from sensors which indicate the level ofremaining fuel in the fuel tank 83, and from a sensor which indicatesthe voltage on the starter battery 84 which provides power to thestarter motor 85 which is used to start the engine 60. Themicroprocessor 70 further provides control signals on output lines 88 toan engine control system 87 which provides output signals on lines 89 tostart the engine 60 by supplying power from the battery 84 to thestarter motor 85, and to control the speed of the engine. Electricalpower for running the engine and recharging the battery 84 may beprovided from a small alternator charger 90 driven by the engine. Themicroprocessor may also provide output control signals on a line 86 toan alternator controller 91 which supplies current to the field windingof the alternator 62 to control the output voltage provided from thealternator and thereby regulate the output voltage on the output lines41 and 42. Alternatively, the output voltage on the lines 41 and 42 (oron the bus lines 43 and 44) may be fed back directly to the alternatorand compared with a reference in a conventional fashion in thecontroller 91.

The engine 60, which acts as the prime mover in the power supply system,is preferably sized to support the shaft load required by the alternatorsystem. Although the engine 60 may typically be a gasoline poweredengine (e.g., an ONAN Gas Electric Model P218), the engine may beadapted to use other fuels, such as liquid petroleum, diesel, kerosene,natural gas, and so forth. The engine is preferably of standard designutilizing automatic choking and fuel management devices to allowunattended operation, and the construction and operation of such enginesis well known in the art. The engine is selected to provide adequateshaft torque to produce prescribed output power over a relatively widespeed range.

The alternator is coupled to the output of the engine either directly orthrough belt drive to provide torque conversion. The alternator ispreferably polyphase, having a rotary field winding with a minimalcurrent commutator and which is adapted to drive low voltage, highcurrent DC loads such as, for example, alternators adapted for DCelectric arc welders, available from Miller Electric ManufacturingCompany and other manufacturers. The armature winding or output windingis stationary, with no brushes required in the output. The armaturewinding is preferably a high frequency (e.g., approximately 100 Hz)polyphase winding (typically three phase), selected to produce highquality DC after rectification. If desired, a separate low frequency (50or 60 Hz) single phase winding may be added to supply alternatingcurrent power to accessories. The output voltage of the armature windingis controlled by the current supplied to the rotating field windingthrough a slip ring commutator. The control of the alternator fieldwinding may be by a conventional feedback controller 91, such as thoseused in arc welding power supplies, or under the control of themicroprocessor 70 which monitors the DC bus voltage on the DC bus lines43 and 44 and provides appropriate feedback control signals to the fieldwinding to maintain the desired output voltage.

The battery or batteries 45 will be selected based on a particularapplication. For example, the main battery 45 may be a multiple celledseries or series-parallel connection of individual batteries, which areconnected together to produce the desired voltage and ampere-hourrequirements of the load. For a given telecommunication or other DCpower load installation, the provision of the auxiliary power supply 40allows the battery 45 to be sized smaller than would otherwise berequired to adequately handle the power requirements of the system. ForUPS operation, the battery may be sized to carry the critical loadthrough short term outages, with the auxiliary power system 40 supplyingpower during prolonged outages.

The rectifier 64 comprises polyphase solid-state rectifiers whichconvert the alternator output voltage to direct current. The filters 76may be formed in a conventional manner of L-C elements to remove thehigh frequency ripple to provide a clean, low-ripple direct current onthe output lines 41 and 42 to the DC bus lines 43 and 44. Additionalfilters may be connected to control electromagnetic interference.

The voltage sensing on the output lines 41 and 42 (or the DC bus lines43 and 44 to which the output lines are connected) may be done bothinternally or externally. Internal sensing provides feedback to thealternator voltage regulator circuitry from the output terminals tomaintain the output voltage regulated to a reference. External sensingprovides feedback to the alternator voltage regulator from either thebattery terminals--maintaining a precise voltage at the battery--or fromthe input terminals at the connected load. The latter connectionmaintains the potential at the load end of the cables. By utilizingexternal sensing, compensation is automatically provided for voltagedrops in the cable connectors, thereby maintaining the prescribedvoltage at the load points at which the voltage sensors are located.Preferably, the user can select the point at which voltage sensing isaccomplished. When external sensing is used, the generator outputvoltage is automatically adjusted so that a predetermined regulatedvoltage appears at the battery terminals, thereby compensating for thevoltage drop in the connecting cables 41 and 42 between the auxiliarypower system 40 and the batteries. Where a telecommunication system isthe load, the sense lines can be connected at the input terminals of theload, thereby automatically correcting for the voltage drop in thecables from the battery bank to the load if long cables are requiredbetween the battery bank and the load.

The microprocessor 70 also preferably monitors the auxiliary powersupply output voltage and load current. If the output voltage becomesexcessive, an alarm is sounded which can be detected by the operator,and a further increase of output voltage to a trigger level (e.g., 62volts for a full charge battery voltage of 56 volts) causes themicroprocessor to shut the system down, thereby protecting the batteries45 from damage. The microprocessor may also monitor the load current andlimits the load current to a safe value. Fuses are provided between thepower system 40 and the output lines 41 and 42 to further provideprotection for current overloads. The battery 45 voltage is alsopreferably monitored and the engine operation is controlledappropriately. When the power system of the invention is connected to abank of telecommunication supply batteries, during charging an alarmwill be triggered followed by turn-off when the temperature compensatedvoltage reaches the prescribed level. At this point, the power providedfrom the auxiliary power system 40 is not required, and the engine isshut-off. For UPS applications, the load current is sensed and when theload current decreases to a small value (a default setting, such as 10amperes or less) the system may interpret this as an inverter shut-down,indicating that commercial line power has returned, and thereafter theengine will automatically be shut down.

The controller includes the microprocessor 70 (e.g., an NEC 7810 8 bitmicroprocessor) with ancillary firmware in the PROM 71 and conventionalcontrol circuitry. Preset values for various engine and operatingparameters are set to default values in the PROM, with these presetvalues determining the operation of the system. Although many parametersand calibration constants can be preprogrammed, preferably these canalso be reprogrammed in the field but with parameters and constantsmaintained secure by utilizing password control.

The display 75 may be a high visibility display, for example, of thevacuum fluorescent type, which provides the operator with significantinformation concerning the operation of the system, such as outputvoltages, currents, operating times, default values, and a functionallog indicating the current state of the system and the history of thestate of the system.

The microprocessor can communicate with the UPS 47 through an RS232 porton lines 77, and may communicate with external remote terminals via theRS232 port or an RS485 interface to the remote devices 76.

The present invention provides an auxiliary power system having a highreliability engine/generator set by appropriate exercising of theauxiliary power system and by monitoring of system conditions during thetime that the system is being exercised and during actual power supplyoperation. The computer controller 70 within the auxiliary power systemmonitors the time elapsed since the last turn-on of the engine 60, whichmay have occurred during an exercise operation or during actual powersupply operation. If the time elapsed exceeds a predetermined interval,the microprocessor controller 70 starts the engine 60 by providing asignal on the lines 88 to the engine control 87 to run the engine 60 andgenerator 62 set with power disconnected from the DC lines 41 and 42 andthe bus lines 43 and 44. The engine is run for a time sufficient toproperly exercise the engine 60 and maintain adequate lubrication andconditioning of moving parts in both the engine 60 and the generator 62.The length of time of running of the engine 60 may be predetermined toachieve a desired system operating condition such as engine temperature.During the time that the engine is operating, the microprocessorcontroller 70 preferably monitors several conditions of the engine 60and generator 62, including the date and time of the exercise cycle, theDC output voltage from the generator 62, the remaining fuel level in thefuel tank of the engine from the fuel sensor 83, the battery voltage ofthe cranking battery 84 that provides the cranking power to turn on theengine and the engine block temperature, oil pressure, and the ambienttemperature, and the microprocessor controller 70 may also monitorconditions of the DC bus line, such as the voltage across the DC buslines 43 and 44, and thereby the condition of the main storage battery45 supplying the UPS 47 or a DC load (not shown in FIG. 7). Duringexercise engine operation, the controller 70 stores the values of thesystem conditions that were monitored in non-volatile memory such as thePROM 71 and makes such values available for read-out, either by anoperator at the site of the auxiliary power system on the display 75, orthrough telemetry to a remote location at remote devices 76. Moreover,the controller 70 preferably compares the monitored system conditionswith predetermined set point conditions and provides an error or warningsignal if the sensed conditions are outside of the boundaries specifiedby the set points, for example, by monitoring the DC voltage output ofthe rectifier 64 and the filter 67, provided on lines 116 and 117 to thealternator control 91 and on the lines 86 to the microprocessorcontroller 70, while the engine 60 is running, and providing a warningsignal to the operator if the output voltage is above or belowpredetermined limits. This warning may be provided through an audible orvisual signal (or both) provided to the operator at the site via thedisplay 75 or remotely by telemetry to the remote devices 76. Thesensing of system condition values which would indicate a seriousmalfunction of the system, such as over-temperature of the engine 60, orvery low fuel level, or deficient generator output voltage, will resultin the controller 70 shutting down the auxiliary power system anddisconnecting it from the DC lines 41 and 42 so that no damage is doneeither to the auxiliary power system or to the components connected tothe DC bus lines. Such monitoring and control of the auxiliary powersystem operation is carried out both during the exercise cycling of theengine and during power supply operation where power is being providedto the DC bus lines.

As noted above, the auxiliary power system includes a cranking battery84 and a starter motor 85, to which the output of the cranking batteryis supplied during starting. The microprocessor controller 70 monitorsthe voltage of the cranking battery and provides a warning, as on thedisplay 75, if the cranking battery voltage drops below a predeterminedlevel and starts the engine 60 for a predetermined period of time if thecranking battery voltage drops below a selected level. The alternatorbattery charger 90 acts as a power supply driven by the engine 60 forproviding charging current to the cranking battery during running of theengine 60 to charge the cranking battery 84.

An exemplary graph of the voltage across the DC bus lines 43 and 44 atthe battery 45 during a cycle in which the power from the power grid isinterrupted and then restored is shown in FIG. 8. In the section of thegraph labeled A the batteries are floating at full charge and the UPSsystem may be conditioning line power to support the critical load withthe power grid functioning normally. At point B the line power fails andthe UPS switches to supply power to the critical load from the battery.The battery voltage begins to fall with an exponential decline. However,at this point in time the auxiliary power system 40 is not activated. Asthe battery voltage continues to fail, it passes a selected point C(e.g., 46 volts on graph of FIG. 8) and the microprocessor 70 provides acontrol signal to the engine controller 87 to start the engine of theauxiliary power supply. However, at this time the output of thealternator is not provided to the DC bus lines. Thus, the voltage acrossthe DC bus lines continues to decline as shown by the section labeled Din FIG. 8. The time during which the engine is running without powerbeing delivered from the alternator is selected to allow the engine towarm up to the desired operating temperature before it is loaded. Thisperiod of time may vary depending on the engine design, but typicallywill be about 30 seconds. After the warmup interval has elapsed, themicroprocessor provides a signal to the alternator control 91 to providethe rectified output of the alternator to the DC bus lines at the timepoint E, which substantially immediately raises the battery voltage tothe point labeled F, e.g., from about 45 volts to about 52.5 volts asshown in FIG. 8. This is a voltage less than the full charge voltage(e.g., 56 volts) of the battery. At this time, DC power is provided fromthe auxiliary power system 40 to the UPS to be converted to AC power tothe load, and further power is provided from the system 40 to thebattery to charge the battery to about 80% of its full charge. Becausethe DC bus voltage is limited to less than the full charge voltage ofthe battery, the auxiliary power system cannot overcharge the battery.

The auxiliary power system 40 continues to provide power to the UPS aslong as necessary, as illustrated by the constant line labeled G in FIG.8. When the commercial line power returns, the UPS switches frominverter operation and functions only to condition line power for thecritical load. The microprocessor senses the drop in current demand onthe DC bus lines and disconnects the alternator from the DC bus linesand turns off the engine. The battery charger within the UPS system isactivated to supply power from the power grid, as shown at the point H,which raises the voltage on the DC bus lines to the charging voltage.The voltage across the DC bus lines increases in a decreasingexponential fashion, as indicated by the line I in FIG. 8, as the UPSbattery charger brings the batteries back up to full charge using powerfrom the power grid.

A schematic circuit diagram of an exemplary output voltage controlcircuit for the alternator 62 is shown in FIG. 9. The voltage-currentregulator 91 provides control current on lines 100 to the field windingof the alternator 62 to maintain a desired output voltage across theoutput lines 41 and 42. The polyphase (e.g., three phase) output of thealternator 62 is provided on output lines 63 to the rectifier 64 whichis illustratively shown as being composed of a full bridge of rectifyingdiodes 102 with parallel capacitors 103. The output of the rectifier 64on the output lines 66 is provided to a filter section 67 asillustratively shown in FIG. 9 as composed of a first parallelcombination of a capacitor 104, resistor 105 and varistor 106 connectedbetween the output lines 66, a series connected diode 107 with parallelcapacitor 108 to prevent backflow of current into the rectifier from theDC lines 41 and 42, a further resistor 109 and varistor 110 connectedacross the lines 66, a series filter inductor 112, a fuse 113, and anoutput filter capacitor 114 connected at the output across the lines 41and 42. The large parallel capacitor 104 (e.g., 50,000 microfarads), theoutput capacitor 114 (e.g., 150 microfarads), and the series inductor112 serve to substantially filter out the ripples in the output of thebridge 64 as well as filtering out high frequency electromagneticinterference. Current backflow into the large filter capacitor 104 isprevented by the diode 107. Feedback of the output voltage is providedby a line 116, extending from connection to the upper conducting line66, and a second conducting line 117 connected to the lower conductingline 66 which is electrically connected to the output line 42. Tomonitor current, a small shunt 120 (e.g., 50 milliohms) is connected inthe return line and a further conducting line 121 is connected to thelower line 66 on the opposite side of the shunt 120 from the connectionof the line 117. Thus, the voltage between the lines 117 and 121 will berelated to the current in the return line. The voltage regulator 91 isconventionally provided with drive current from the alternator 62 onlines 123 and may function in a conventional fashion to control theoutput voltage and current to desired levels in accordance with presetadjustments of the voltage and current in the regulator in a fashionconventional in power supplies of this type, such as power supplies forarc welding machines. For example, the regulator may be set to providean output voltage of 52.5 volts from the rectifier where the fullycharged voltage of the storage battery 45 is 56 volts. If an overcurrentis detected, the regulator 91 can shut down the alternator by cuttingoff the current to the field winding. Alternatively, control signals maybe provided on the control lines 86 from the microprocessor 70 toprovide feedback signals to the voltage-current regulator indicating thedesired voltage or current level to be maintained by the system atpoints in the system other than at the output of the rectifier.

It is understood that the invention is not confined to the particularconstruction and embodiments illustrated herein, but embraces suchmodified forms thereof as come within the scope of the following claims.

What is claimed is:
 1. A power supply system for a telecommunicationssystem comprising:(a) DC bus lines which are connectable to atelecommunications system; (b) a storage battery connected across the DCbus lines; (c) an internal combustion engine and means for responding toa control signal to start the engine; (d) an alternator coupled to theengine to be driven by it and having AC output terminals; (e) arectifier connected to the output terminals of the alternator forrectifying the AC output of the alternator to a DC voltage; (f) e meansfor filtering the DC voltage from the rectifier to provide a filtered DCvoltage to the DC bus lines; (g) means for controlling the alternatorwhen the engine is running to provide a controlled DC output voltagefrom the rectifier and the means for filtering to the DC bus lines sothat the voltage across the DC bus lines is maintained at a selectedvoltage level; (h) a charger connected to receive power from an AC powersystem and connected to supply DC power to the DC bus lines when ACpower is available from the AC power system; (i) control means connectedto monitor the voltage on the DC bus lines for providing a controlsignal to turn on the engine when the voltage across the DC bus linesdrops belows a predetermined value and for controlling the means forcontrolling the alternator for activating the alternator to provide theDC output power from the rectifier and filter means to the DC bus lines.2. The power supply system of claim 1 wherein the voltage across the DCbus lines when the output of the rectifier is connected thereto ismaintained at a voltage level below the nominal open circuit voltagelevel of the battery.
 3. The power supply system of claim 1 wherein thecontrol means senses the current drawn from the alternator on the DC buslines, and wherein the control means turns off the engine when currentis not being drawn from the alternator.
 4. The power supply system ofclaim 1 wherein the control means monitors the time elapsed since thelast turn-off of the engine and if the time elapsed exceeds apredetermined time interval the control means provides a control signalto start the engine and controls the alternator so that no power isdelivered from the alternator to the DC bus lines, and controls theengine to run for a selected period of time to allow the engine toadequately warm up and thereafter shuts off the engine.
 5. The powersupply system of claim 4 wherein the control means includes means formonitoring engine temperature, oil pressure, and fuel level in a fueltank which supplies fuel to the engine, wherein the control means storesthe values of the sensed parameters in a memory, and provides the valuesin the memory for interrogation by an operator and provides an alarm toan operator if a parameter falls outside a predetermined limit for thevalue of the parameter.
 6. The power supply system of claim 1 whereinthe control means includes means for monitoring the filtered DC voltageoutput of the rectifier and filter means while the engine is running andfor providing a warning signal to an operator if the output voltage isabove or below predetermined limits.
 7. The power supply system of claim1 wherein the engine includes a cranking battery and a starter motor towhich the output of the cranking battery is supplied during starting,and the control means includes means for monitoring the voltage of thecranking battery and wherein the control means provides a warning if thecranking battery voltage drops below a predetermined level and startsthe engine for a predetermined period of time if the cranking batteryvoltage drops below a selected level, and wherein the system furtherincludes power supply means driven by the engine for providing chargingcurrent to the cranking battery during running of the engine to chargethe cranking battery.
 8. The power supply system of claim 1 wherein thecontrol means controls the means for controlling the alternator so asnot to supply power to the DC bus lines for a selected period of timeafter the engine has started to allow the engine to warm up, and forthen activating the alternator to provide the DC power from therectifier and the filter means to the DC bus lines.
 9. The power supplysystem of claim 1 wherein the control means includes a microprocessor,an analog to digital converter connected to the DC bus lines to receivethe DC voltage at the battery and providing digital data correspondingto the DC voltage to the microprocessor, the microprocessor providingcontrol signals to the means for controlling the alternator to maintainthe DC voltage at the battery at a chosen level.